diff --git a/Project.toml b/Project.toml
index 08f8197..27d870b 100644
--- a/Project.toml
+++ b/Project.toml
@@ -9,6 +9,7 @@ HTTP = "cd3eb016-35fb-5094-929b-558a96fad6f3"
 JSON = "682c06a0-de6a-54ab-a142-c8b1cf79cde6"
 PyFormattedStrings = "5f89f4a4-a228-4886-b223-c468a82ed5b9"
 Unitful = "1986cc42-f94f-5a68-af5c-568840ba703d"
+Reexport = "189a3867-3050-52da-a836-e630ba90ab69"
 
 [compat]
 julia = "1"
diff --git a/src/AtomicAndPhysicalConstants.jl b/src/AtomicAndPhysicalConstants.jl
index e70e355..0b9808b 100644
--- a/src/AtomicAndPhysicalConstants.jl
+++ b/src/AtomicAndPhysicalConstants.jl
@@ -4,7 +4,8 @@ using PyFormattedStrings
 using Dates
 using HTTP
 using JSON
-using Unitful
+using Reexport
+@reexport using Unitful
 
 include("physical_constants.jl")
 include("atomic_isotopes.jl")
diff --git a/test/runtests.jl b/test/runtests.jl
index c07bf47..e888f38 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -9,30 +9,16 @@ end
 
 @testset "set_units.jl" begin
 
-    # constants should be undefined when setunits() in not called
-    @test !@isdefined c_light
-    @test !@isdefined m_electron
-    @test !@isdefined m_electron
-    @test !@isdefined m_proton
-    @test !@isdefined m_neutron
-    @test !@isdefined m_muon
-    @test !@isdefined m_helion
-    @test !@isdefined m_deuteron
-    @test !@isdefined m_pion_0
-    @test !@isdefined m_pion_charged
-    @test !@isdefined r_e
-    @test !@isdefined e_charge
-    @test !@isdefined h_planck
-    @test !@isdefined mu_0_vac
-    @test !@isdefined eps_0_vac
-    @test !@isdefined kg_per_amu
-    @test !@isdefined eV_per_amu
-    @test !@isdefined N_avogadro
-    @test !@isdefined fine_structure
-    @test !@isdefined classical_radius_factor
-    @test !@isdefined r_p
-    @test !@isdefined h_bar_planck
-    @test !@isdefined kg_per_eV
+    # units should be available to users, including "amu" and "e"
+    # if not availble, an error would be thrown and the test would fail.
+    @test u"kg" == u"kg"
+    @test u"km" == u"km"
+    @test u"amu" == u"amu"
+    @test u"eV/c^2" == u"eV/c^2"
+    @test u"e" == u"e"
+    @test u"C" == u"C"
+    @test u"s" == u"s"
+
 
     #setunits to default units
     setunits()
@@ -161,11 +147,11 @@ end
     H = Species("H", 1, 1, 0, 0, 0)
 
     #mass should be in amu and charge in elementary charge
-    setunits(mass_unit = u"amu")
+    setunits(mass_unit=u"amu")
 
     @test massof(H) ≈ 1.0
     @test chargeof(H) ≈ 1
-    @test massof(H, "kg") ≈ 1.6605e-27
+    @test massof(H, "kg") ≈ 1.6605390671738466e-27
     @test chargeof(H, "C") ≈ 1.602176634e-19